1. Field of the Invention
The present invention relates to a method of manufacturing a thin film transistor, and more particularly, to a method of manufacturing a thin film transistor having a structure in which a lightly doped drain (LDD) region is formed between a source/drain region and a channel region.
2. Description of the Related Art
Thin film transistors (TFT) are used as switching devices in flat panel displays such as organic light emitting displays (OLEDs) or liquid crystal displays (LCDs). A TFT usually includes a semiconductor layer, a gate electrode, and source and drain electrodes, and the semiconductor layer includes source/drain regions and a channel region interposed between the source region and the drain region. The semiconductor layer can be formed of polysilicon or amorphous silicon. Polysilicon is generally used to form semiconductor layers because the electron mobility of the polysilicon is higher than that of the amorphous silicon and thus the semiconductor layer formed of polysilicon is advantageous for high speed operation of devices.
On the other hand, polysilicon thin film transistors have a greater off current than amorphous silicon thin film transistors. To address this problem associated with polysilicon TFTs, a structure in which lightly doped drain (LDD) regions are formed between source/drain regions and a channel region has been suggested. The LDD regions can prevent a rapid increase in the electric current of an electric field between the channel region and the source/drain region. As a result, the off current of TFTs can be lowered and a hot carrier effect (HCE), which appears as the length of a channel of TFTs decreases, can be suppressed, thereby increasing the reliability of the channel. However, in conventional TFT manufacturing processes the photomask process and the etching process are performed separately to form the LDD regions, thereby increasing the number of manufacturing processes and manufacturing costs. Moreover, the interface property of the source/drain region can undergo deterioration when the photomask process and etching process are performed separately.